I just might have the solution for you.
I was facing the exact same issue with Firefox where I could only scroll with two-fingers and single finger selected text.
After a lot of searching I found this Gentoo Wacom page mentioning that the Wacom driver has gesture emulation that causes a problem with Firefox and my Thinkpad X1 Yoga has a Wacom touchscreen.
The fix is to turn off the Wacom gesture setting by creating the following file:
/etc/X11/xorg.conf.d/50-wacom.conf
With this configuration:
Section "InputClass"
Identifier "Wacom class"
MatchProduct "Wacom|WACOM|Hanwang|PTK-540WL|ISDv4|ISD-V4|ISDV4"
MatchDevicePath "/dev/input/event*"
Driver "wacom"
Option "Gesture" "off"
EndSection
Resart and enjoy :)
MOZ_USE_XINPUT2=1
, as in where did you place this command?